Adhesive bonding method



Patented Sept. 5, 1950 ADHESIVE BONDING METHOD Ralph K. Super, Detroit,Mich, auignor to The Tiniken-Detroit Axle Company, Detroit, Mich acorporation of Ohio Application April 4, 1945, Serial No. 588,529

9 Claims. (Cl. 154-1265) This invention relates generally to a methodfor adhesively securing a non-conducting material to a part made ofelectrically conducting material and particularly concerns an improvedmethod for cementing brake linings to metal brake shoes.

Among the advantages of cemented brake linlugs, as compared to rivetedlinings, are: longer wear for linings of the same thickness, increasedbraking area for linings of the same dimensions, and less damage tobrake drums.

During operation of the brake, the cement is subjected to severeconditions of heat and shearing stress. It is desirable, therefore, touse a thermally activated, heat resistant adhesive for bonding thelining to the brake shoe. However, care must be exercised in activatingthe cement to avoid heating the brake lining material above its curingtemperature. In quantity production, the brake shoes must be handledimmediately after attachment of the linings, so it is desirable to avoidexcessively heating the body oi. the shoe while activating th cement.

As the invention is particularly useful for cementing brake linings tobrake shoes, this application of the invention has been chosen forpurposes of the following description. It should be understood, however,that reference to the brake lining is intended to include any part madeentirely or mainly of non-conducting material, and any electricalconductor capable of being inductively heated may be used instead of abrake shoe without departing from the spirit of the invention.

A non-conducting part, within the spirit of the present invention, maybe a part composed entirely of electrically insulating material or maycontain small amounts of conducting material in quantities insuiiicientto make the part electrically conductive. For example, a brake lining ofmolded synthetic resin and asbestos may contain dispersed conductiveparticles or pieces of conductive material for increasing wearresistance, but such does not render it electrically conductive.

It is a major object the invention to provide a method for thermallyactivating an adhesive to bond a non-conducting part to a conductingpart without excessively heating either of the two parts.

An important object of the invention is to provide a method forattaching a brake lining to a brake shoe by thermo-setting a cementbetween the lining and shoe without materially 2 heating the lining orbody of the shoe, and the novel article produced thereby.

Another object of the invention is to provide a highly eilicient methodfor thermally activating an adhesive bond.

A more specific object of the invention is to provide a method forspeedily attaching a brake v lining to a brake shoe in which theadhesive is heat activated .by inductively heating the brake shoesubstantially only atthe surface adjacent the adhesive.

Other and further objects will appear from the following specificationand accompanying drawing, wherein there is shown, for purposes ofillustration, apparatus embodying the invention in its preferred formfor attaching a brake lining to a brake shoe.

In the drawing:

Fig. 1 is an elevation view, partially in section, showing apparatus forattaching brake linings to brake shoes in accordance with thisinvention;

Fig. 2 is an enlarged section through the base portion of the apparatusshowing the arrangement of the brake shoe and the brake lining also insection;

Fig. 3 is a top plan view of the base portion of the apparatus of Fig. 1showing the arrangement of an induction coil inrbedded therein; and

Fig. 4 is a transverse section through the center of the induction coil.

In accordance with th invention in its pre- .ferred form, an adhesive isplaced between mating surfaces of the brake lining (non-conducting part)and the brake shoe (conducting part). The surfaces to be joined are thenplaced under considerable pressure and the brake shoe is heated in arestricted zone along the adhesive surface to thermally activate theadhesive and secure the bond. This heating may be acomplishedinductively by concentrating a high-frequency electro magnetic flux inthe skin of the brake shoe lying along the surface to be cemented.Preferably, power for heating the brake shoe is applied for only a shorttime interval, so that the total heat may be dissipated withoutexcessively heating the whole brake shoe or the lining.

When a relatively thick lining is used, its stillness may tend to pullthe lining away from the shoe. To avoid this separation, the lining maybe rendered more flexible by placing on or more cuts across the brakingsurface of the lining, leaving only a relatively thin flexible web incontact with the brake shoe.

Referring to the drawing, there is thown in Fig. 1 one form of apparatuswhich may be used 3 in practicing the invention to cement a brake liningll onto a brake shoe II. A brake shoe of this type is usually a metalcasting having a smooth cylindrically shaped surface I! (Fig. 2), towhich the brake lining H is to be attached, and provided with necessaryfittings and I5 for mounting and actuating the brake. The brake liningis preferably formed in two segments l8 and ll of a molded plasticcompound including asbestos. These segments are arranged adjacent eachother to provide a friction surface covering substantially the entiresurface l3 of the brake shoe.

In attaching the brake lining I l to the shoe [2, an adhesive is placedbetween the surfaces to be bonded. This may be accomplished by coatingnect the high-frequency generator 23 to the induction coil 21, theconcentrated high-frequency electromagnetic field produced by the coil21 induces heating currents in the metallic brake shoe l2, which isusually of iron. Due to the skin eflect of high-frequency electricalcurrents, the heating current induced in the brake shoe are restrictedmainly to the skin of the brake shoe; Therefore, only that narrow zoneof the brake shoe l2 which lies along the bonding surface I3 isinductionally heated by energy from the coil 21. Since this zone isadjacent the bonding surfaces of the brake shoe and lining,

- heat is conducted to the cement or adhesive and a suitable adhesive onthe surface ll of the shoe l2 and/or the surfaces of the segments I! andI! which are to be bonded to the shoe. Preferably, the surface l3 of theshoe and also the surfaces of the segments l6 and H are coated with aplastic type cement, such as a thermosetting resin.

After the coating of adhesive or cement has dried, the two segments [6and H are placed inarecess llformedinabedorbase I! ofan arbor press 2|.The bed I! is made of suitable electrically insulating material. such ascement, Bakelite or other plastic, and the recess II has its surfaceshaped to conform to the friction surface of the brake lining H when itis applied to the brake shoe l2. To insure a uniform bond between thelining and the brake shoe, pressure is applied to the brake shoe 12, asby a piston rod 22, which may be actuated by piston 23 in pneumaticcylinder 24. The pressure applied to the brake shoe may be controlled bya valve 25 in compressed air line 26, which supplies pressure fluid tothe cylinder 24. It has been found that a pressure in the neighborhoodof 100 pounds per square inch is satisfactory to produce a uniform bond.

For purposes of heating the brake shoe to set the cement, an inductioncoil 21 is imbedded in the insulating block ID. This coil consists of anumber of turns of hollow metal tubing wound in spiral fashion with allof the turns lying in a surface of revolution having a radiuscorresponding to that of the recess ll. Thus, all of the turns of theinduction coil lie substantially flush with the surface of the recessI8, and therefore have a shape which conforms to that of the brakelining H and the bonding surface I! of the brake shoe l2. Thisarrangement of the coil is such that, when it is supplied with asuitable current, it produces a concentrated electromagnetic field ofsubstantially uniform density and coextensive with the surfaces of thelining H and the brake shoe I2 which are to be bonded together.

In order to heat only a restricted zone of the brake shoe l2 which isadjacent the bonding surface 13, the induction coil 21 is excited from ahigh-frequency generator 2|, which may be supplied with power from asuitable electrical source 2! and is of a conventional oscillator andpower amplifier type for producing electrical oscillations having afrequency of, for example, two

megacycles per second. This high-frequency energy from the generator 23may be supplied by conductors 3| and 32 through a push-button typetiming switch 33, of conventional type, to terminal conductors 34 and 35of the hollow tubing forming the induction coil 21.

'Whenthetimingswitch 33 isactuatedtocom raises the temperature of thecement until polymerization takes place. Polymerization of suitablethermo-setting plastic cements now available for this purpose takesplace at about 325- 350 F. It is only necessary, therefore, to applyhigh-frequency energy to the induction coil until the cement is heatedto its setting temperature. with a high-frequency generator having acapacity of 20 kilowatts, it has been found that, for average size brakeshoes, the cement is polymerized and the lining bonded to the shoewithin a time period of approximately six seconds.

Since heat is induced only in .a restricted zone of the brake shoe andthe heating period is relatively short, the total heat may be dissipatedthrough other portions of the shoe and also through the lining withoutoverheating either the shoe or the lining. It is possible to handle thebrake shoe, with the lining attached, immediately after the switch 33disconnects the high-frequency generator from the induction cell. Thistiming switch is set to automatically disconnect the generator from thecoil after the time interval necessary to set the cement. or course,this time may vary for different operating conditions and sizes of brakeshoes, so the timing switch 33 is preferably adjustable to provide fordifferent time intervals.

The lining H, being formed of molded plastic material, must not beheated above its curing temperature, which is about 450 F. for standardbrake linings. To keep the induction coil 21 cool and to carry off heatfrom the lining II, a

cooling fluid, such as water, may be circulatedthrough the hollowconductor forming the windings of the coil. For this purpose, aconventional pump 37 is connected through suitable conduits 39 and H andcouplings 42 and 43 to the terminal conductors 34 and 35 of the coil 21.It will be necessary, of course, to plug the terminal conductors 34 and35 between the couplings and the switch 23 to avoid circulation ofliquid away from the coil.

When thick brake linings are applied to the brake shoe, they have atendency to pull away and break the cement bond between the lining andthe shoe due to stresses set up in shaping the lining to the shoe. Toavoid this, a saw cut, such as that shown at 46 and 41, in the segmentsl6 and H may be placed across the face of the lining, leaving only athin flexible web cemented to the shoe.

As will be apparent from the foregoing description, the presentinvention provides for rapid consumed solely during the :short heatinginterval, the efficiency of apparatus-embodying the invention isexcellent. Quantity production of brake shoes with cemented liningsisgreatly facilitated because the bonded parts may be removedimmediately after heating without the use of special handling equipment.

If the induction coil 21 is larger than the surface of the brake shoe tobe heated, stray fields may be eliminated by masking the edges of thecoil with suitable high-frequency shielding material. Brake shoes invarious ranges of sizes may be accommodated by simply changing the basein the arbor press. Thus, a series of bases, each with a recess and coilfor particularly shaped brake shoes, may easily be placed in the pressand coupled to the high-frequency generator.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all .respects asillustrative and not restrictive, the

scope of the invention being indicated by the appended claims ratherthan by the foregoing description, and all changes which come within themeaning and range of equivalencey of the claims are therefore intendedto be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

l. in a method of bonding an electrically conductive member to a,substantially electrically non-conductive member which has been cured ata predetermined temperature to attain a desired physical condition, thesteps of assembllng said members under pressure with a layer ofthermo-setting adhesive between coextensive surfaces of said members,subjecting said assembly to a concentrated high frequencyelectromagnetic ileld for speedily heating by induction a thin surfacezone of said conductive member adjacent said adhesive layer for settingsaid adhesive to bond the members together at said surfaces andmaintaining the temperature at said surfaces below that which will altersaid physical condition.

2. In a method of bonding a cured preformed brake lining element to ametallic brake shoe, the steps of assembling the shoe and lining underpressure with a layer of thermosetting adhesive between coextensivesurfaces and subjecting the assembly to a high frequency electromagneticinduction field for setting the cement while maintaining the temperatureat said surfaces below substantially 450 F.

3. The method of securing an electrically conductive part to a partwhich is substantially nonconductive electrically which comprisesplacing the parts together under pressure with a thermosetting adhesivebetween coextensive surfaces to be joined, and providing a highfrequency field of electromagnetic energy for inductively heat- :ingsubstantially only the adhesive contacting surface of said electricallyconductive part for a predetermined short interval to thermally set saidadhesive and bond said parts together, while maintaining saidelectrically non-conductive part below a predetermined temperature.

4. The method of attaching a surface of a heat treated part which issubstantially electrically non-conductive to a coextensive surface of anelectrically conductive part of substantial mass, which comprisesproviding between said surfaces a layer of thermo-setting ing a' highfrequency electromagnetic field for.

8. adhesive, pressing said surfaces togethe z. and applying a highfrequency electromagnetic field for inductively heating saidelectricahy-, .con -I ductive part in only a relatively narrow zone atits adhesive contacting surface for a predetpr mined short period tothermally set the adhesive while maintaining the temperature at said.zone below a predetermined level corresponding to the temperature atwhich said electrically non-conductive part was heat treated.

5. The method of cementing apreformed heat cured brake lining to ametallic brake shoe which comprises assembling the brake lining on the.brake shoe under pressure with a thermo-setting' adhesive between thesurfaces to be joined, applyinductively heating said brake shoe only ina narrow zone adjacent its adhesive contacting surface to thermally setthe adhesive and bond the lining to the shoe, and maintaining thetemperature at said zone below the curing temperature of said lining.

6. The method of attaching a heat cured brake lining of a material thatis substantially electrically non-conductive to an electricallyconductive brake shoe by cementing a surface of the lining to a surfaceof the shoe, which comprises coating at least one of said surfaces witha thermo-setting adhesive material, pressing said surfaces together, andheating said brake shoe by electromagnetic induction only in a narrowzone adjacent its adhesive material contacting surface sufliciently tothermally set the adhesive material, while maintaining the temperatureat said zone below the curing temperature of said lining.

7. The method of attaching a substantially electrically non-conductivepart to an electrically conductive part of relatively large mass byadhesively securing a surface of the non-conductive part to a surface ofthe conductive part, which comprises pressing the parts togetheif with athermo-setting adhesive between the surfaces to be joined, andsubjecting said parts to a concentrated field of high frequencyelectromagnetic energy with said surface of the conducting part nearerto said source of energy than other portions of said conducting part forinductively heating only a relatively thin zone of said conductive partadjacent said surfaces to thermally set the adhesive while maintainingsaid nonconductive part below a predetermined temperature.

8. The method of attaching a preformed heat cured brake lining to ametallic brake shoe by cementing a surface of the lining to a surface ofthe shoe, which comprises pressing said surfaces together with athermo-setting adhesive therebetween, and for a very short time intervalsubjecting the lining and the shoe to a concentrated field of highfrequency electromagnetic energy with said surface of the shoe nearer tothe source of said energy than other portions of said shoe forinductively heating only a narrow zone of said shoe adjacent saidsurface suflicient to thermally set the adhesive while maintaining thetemperature at said zone below the curing temperature of said lining.

9. In a method of adhesively bonding a surface of a preformedsubstantially electrically non-conductive heat cured brake liningelement to the surface of a metal brake shoe, the steps of assemblingsaid lining and shoe in desired relation with said surfaces adjacent andsepa= rated only by a him of thermo-setting adhesive,

I andsubjeetlnzsaidmemhlytoaqmekhigh power burst of hieh frequencyelectromagnetic 'luductionenerzyinsuchmannerastoreisethe temperature ofsubstantially only said brake shoe surface sumciently high to speedilyset said adhesive to securely bond said surfaces together whilemaintaining the temperature at said surfaces below the curingtemperature of said lininz.

RALPH K. SUPER.

REFERENCES CITED The following references are of record in the me 01this patent:

UNITED STATES PATENTS Number Name Date 1,882,819 Bluhm Aug. 28, 19281,806,846 Pox May 28. 1931 01m REFERENCES Ber. No. 229,798, Baseler (A.P. 0.), published May 11, 1943.

Coils, Oct. 1943 issue of Electronics, pp. 112. 113, 299. and 300.

1. IN A METHOD OF BONDING AN ELECTRICALLY CONDUCTIVE MEMBER TO ASUBSTANTIALLY ELECTRICALLY NON-CONDUCTIVE MEMBER WHICH HAS BEEN CURED ATA PREDETERMINED TEMPERATURE TO ATTAIN A DESIRED PHYSICAL CONDITION, THESTEPS OF ASSEMBLING SAID MEMBERS UNDER PRESSURE WITH A LAYER OFTHERMO-SETTING ADHESIVE BETWEEN COEXTENSIVE SURFACES OF SAID MEMBERS,SUBJECTING SAID ASSEMBLY TO A CONCENTRATED HIGH FREQUENCY ELECTRO-